Hydraulic wheel slip control



1965 J. w. CARTER ETAL 3,217,82

HYDRAULIC WHEEL SLIP CONTROL Original Filed May 16, 1963 5 Sheets-Sheet1 INVENTORS Joy/v 14 6A RTER 6'0/PDON 14 L/oH/vsolv BY POBERT N. S TEDMAN AT TORN E YS' 1965 J. w. CARTER ETAL 3,217,26

HYDRAULIC WHEEL SLIP CONTROL Original Filed May 16, 1963 5 Sheets-Sheet2 INVENTORS Joy/v W. CAR TER GORDON W JOHNSON BY POBERT AA STEDMAN IATTORNEYS L m um TC n mww TL m AH CW .0 wm .U m w H Nov. 16, 1965 5Sheets-Sheet 3 Original Filed May 16, 1965 1 VENTORS JOHN CARTER60/?00/\/ 14/ JOHNSON ATTORNEYS Nov. 16, 1965 J. w. CARTER ETAL 3,

nynmumc WHEEL SLIP CONTROL Origihal Filed May '16, 1963 5 Sheets-Sheet 4INVENTORS JOHN M! 14 RTER GORDON WJOHNSON ROBERT N. STEDMAN ATT'O NEYS 1& O o W I M Nov. 16, 1965 J. w. CARTER ETAL. 3

HYDRAULIC WHEEL SLIP CONTROL Original Filed May 16, 1963 5 Sheets-Sheet5 1 VENTORS JOHN CARTER Gama/v W JOHNSON BY ROBERT N. STEDMAN ATT RNBYS3,217,826 HYDRAULIC WHEEL SLIP CONTRGL John W. Carter and Gordon W.Johnson, Peoria, and

Robert N. Stedman, Chillicothe, 111., assignors to Caterpillar Tractor(10., leoria, 111., a corporation of California Continuation ofapplication Ser. No. 280,793, May 16, 1963. This application Dec. 17,1964, Ser. No. 419,630 8 Claims. (Cl. 180-77) The present inventionrelates to means for controlling the relative speed between the drivenwheels and nondriven wheels of a vehicle.

This application is a continuation of application Serial No. 280,793,filed May 16, 1963, and now abandoned.

The present invention is particularly applicable for use with vehiclesof the earth moving variety wherein slipping of the driven Wheels is notan uncommon occurrence. Modern-day earth moving vehicles are becominglarger and more powerful to increase efliciency and thereby reduceconstruction costs. These large vehicles require the use of very largetires which represent a substantial portion of the machines initial costand operating overhead. Thus, wheel slippage with accompanying excessivetire wear is so economically hazardous that crawler type tractors areoften employed in pushing arrangement with the wheeled vehicle as thesole source of motivating power. Since this is not the most eflicientmanner of operating earth moving vehicles, a dependable means foreliminating wheel slippage is considered of the utmost importance anddesirability.

Accordingly, it is an object of the present invention to provide meansfor detecting and controlling the slippage of the power driven wheels ofa wheeled vehicle.

It is another object of the present invention to provide hydraulic meansfor sensing and controlling the slippage of driven wheels of an earthmoving vehicle.

It is a further object of the present invention to provide hydraulicmeans for detecting and controlling the slippage of the tractor wheelsof a tractor driven scraper, of the wheels of a scraper having its ownpower source driving the scraper wheels, and of the driven wheels of afour wheel tractor.

Further and more specific objects and advantages of the presentinvention will be made apparent in the following specification wherein apreferred form of the invention is described by reference to theaccompanying drawings.

In the drawings:

FIG. 1 is a generally schematic illustration of a tractor drawn scraperwith the hydraulic wheel slip control device of the present inventionshown in controlling arrangement with the engine speed regulation means;

FIG. 2 is a partial cross sectional illustration of hydraulic motormeans and the non-driven wheels of the scraper of FIG. 1;

FIGS. 3 and 4 illustrate alternate embodiments of the present inventionas employed to prevent the slippage of the power driven wheels of ascraper; and

FIG. 5 illustrates an embodiment of the invention as employed on a fourwheel tractor.

Referring now to FIG. 1, a tractor 11 having a pair of power drivenwheels 12 (only one of which is shown) is attached to and provides theprimary motive force for a scraper 13. Scraper 13 has a pair ofnon-power driven wheels 14 (only one of which is shown) which always3,217,826 Patented Nov. 16, 1965 travel at the ground speed of thevehicle and thus provide a measure thereof.

During loading operations in which earth is gathered by the scraper bowl16, it is not uncommon for the power driven wheels 12 to break loosefrom the terrain over which they are traveling and thus be driven at aspeed greater than that at which the vehicle is moving (as indicated bythe speed at which wheels 14 are moving). As mentioned above, this wheelslippage problem is of such concern that it is not uncommon for thetractor 11 to be completely neutralized during scraper loadingoperations and a crawler tractor, a portion of which is shown at 17, tobe employed as the source of motivating power by pushing the scraperfrom the rear.

The present invention provides means for inhibiting the slipping ofwheels 12 by providing a control which decreases the speed of the engineof the tractor 11 when the speed of the tires 12 exceeds the groundspeed by a preset amount. More particularly, a hydraulic pump 18 isdriven by the tractor transmission so as to be operated at a speed whichis proportional to the speed of wheels 12. Pump 18 draws hydraulic fluidfrom a sump 19 and delivers it via conduits 21 and 22 to a fluid motor23 associated with the wheels 14 of scraper 13. A conduit 24 leading toa hydraulically actuated servo 26 and a conduit 27 leading to a manuallyoperable valve 28 communicate with one another as well as with conduits21 and 22.

During operation of the tractor drawn scraper in which wheels 12 and 14are both operating at ground speed (wheels 12 not slipping) pump 18 willdeliver hydraulic fluid through conduit 22 to motor 23 which will beoperated by the fluid passing therethrough to a conduit 29 whichcommunicates between motor 23 and sump 19. The motor 23 is mechanicallyconnected through a gearing arrangement generally indicated at 31 (FIG.2) to one of wheels 14 such that the speed of motor 23 is restricted toa speed which is proportional to the speed at which Wheels 14 aretraveling. The pump 18 furnishes sufiicient hydraulic fluid in conduit22 to drive the motor 23 near its maximum operating speed due to itsmechanical connection with the wheel 14. Under these conditions (nowheel slipping) fluid will circulate through conduit 22, motor 23, andreturn conduit 29 without pressure in excess of normal operatingpressure being built up in conduit 22. If the wheel 12 begins to slip,however, the output from pump 18 will increase while the rate of fluidflow through motor 23 will remain constant. This will give rise to anincreasing pressure in conduit 22 and therefore in conduit 24 as well.

Servo 26 is disposed between the vehicle operators manually actuatedlinkage 32 and overriding linkage 30. During normal operation of thevehicle (no wheel slippage) the pressure in conduit 24 will not besufficient to actuate the servo 26 and the operators linkage 32 willdetermine the speed of the vehicle engine. When wheel slippage occurs,however, and the pressure in conduit 24 increases a spring biased piston33 will be urged against a biasing spring 34 so as to retract andthereby operate linkage 30 which is connected to piston 33 by piston rod36. The clockwise rotation of linkage 30 due to retraction of piston 33overrides the vehicle operators control and causes the vehicle engine toreduce its speed. The speed of the vehicle will continue to be reduceduntil the power delivered to wheel 12 is insutficient to cause it toslip and the ground speed of wheel 12 once again becomes equal to thatof wheels 14. The amount of wheel slippage which it is desired totolerate can be easily controlled by adjustment of the spring constantof spring 34.

It is seen from the foregoing discussion that in order for the hydrauliccontrol system to accurately determine when the speed of the engineshould be decreased it is necessary that a ground speed reference beestablished somewhere in the system. Particular reference to FIG. 2 willshow how the motor 23 provides this function. Motor 23 is secured withinan axle 14a which carries one of wheels 14. The bracket 37 whichconnect-s motor 23 to axle 14a has formed on one end thereof a ring gear38. A pair of planet gears 39 are carried by wheel 14 through theirshafts 41 and mesh with ring gear 38. Planets 39 also engage a sun gear42 which is connected through a one-way clutch mechanism 43 to the shaft44 of motor 23. Thus, the rotation of wheel 14 causes planet 39 torevolve around ring gear 38 which acts as a reaction member and enablesthe planets to drive sun gear 42. The speed of sun gear 42 is thusproportional to the speed of wheel 14 which represents the ground speedof the tractor-scraper vehicle. Since the fluid which passes throughline 22 from pump 18 will want to drive shaft 44 at a speed greater thanthat at which the shaft is driven by sun 42, the sun 42 and shaft willbe connected through one-way clutch 43 (which is designed to provideconnection when the speed of sun 42 is less than that at which shaft 44wants to be driven, and disconnects sun 42 from shaft 44 when the Wheel14 drives the shaft 44 faster than the hydraulic fluid delivered theretodoes). As seen from the foregoing description the motor 23 provides adevice in the hydraulic system which represents ground speed and whichis not a function of the speed of the engine of vehicle 11 or the outputof pump 18. Pump 23 has not been shown in detail because pumps which arecapable of providing the function described are well known in the artand of various designs, none of which are meant to be limiting on thepresent invention.

Referring to FIGS. 1 and 2, manually operable valve 28 communicates withsump 19 through a conduit 48 such that a fluid bypass is formed directlybetween sump 19 and pump 18 via conduits 21, 27 and 48 when the slipcontrol mechanism is not to be employed. Thus, when the vehicle is to bemoved from one working location to another working location atrelatively high speed, valve 28 is positioned to divert the majorportion of the fluid pumped by pump 18 and thus prevent the variouscomponents of the system from being operated beyond their normal limits.If the vehicle should be moved at relatively high speeds without valve28 being placed in the non-operative position, the one-way clutch 43will automatically overrun the motor shaft 44 at a given speed(determined by the motor characteristics, pump charac teristics, etc.)and thereby effectively disconnect the shaft 44 from the sun gear 42.

Referring to FIG. 3,. a two wheel tractor 51 having a pair of enginedriven wheels 52 is connected to a scraper 53 having a pair of enginedriven wheels 54. Because of the difliculty which the operator of such avehicle has in seeing the rear wheels 54, it is highly desirable toprovide means by which slippage of wheels 54 is detected and controlledto prevent excessive wear of the tires. To accomplish this purpose afluid pump 56 is mechanically associated with the engine which driveswheel 54 so as to be driven at a speed which is proportional to thetraveling speed of wheels 54, while a pump 57 is associated with theengine of tractor 51 and operates at a speed which is proportional tothe speed of wheels 52. A conduit 58 connects the output of pump 56 to amanually operable valve 59 which leads to the input of pump 57 through aconduit 61 when the valve is in one position (the position shown bysolid lines) and to a return line 61 via a conduit 63 when the valve 59is in the bypass position (shown in dotted lines). Line 58 communicateswith a conduit 64 which leads to a serve 66 which controls linkage 67which controls the speed of operation of the engine which drives wheels54. When valve 59 is in the operative position (that shown in solidlines) and wheels 54 are traveling at ground speed (as opposed toslipping) pump 56 will deliver approximately the same amount of fluidwhich pump 57 will pump through a conduit 68 to return line 62 whichleads to sump 69 from which pump 56 draws its working fluid. Under theseconditions pressure in conduit 58 and thus conduit 64 will remainrelatively constant and below the pressure necessary to actuate servo 66to operate linkage 67. If wheels 5'4 begin to slip, however, pump 56will be driven at a greater speed than pump 57 and thus provide morefluid to pump 57 than pump 57 discharges through conduit 68. This willcause a build up of pressure in conduits 58 and 64 and result in servo66 operating linkage 67 which will in turn reduce the speed of operationof the engine driving wheels 54 until the speed of the wheels isreturned to the ground speed. When valve 59 is positioned to bypassfluid through conduit 63 it is seen that a parallel path still existsthrough conduit 61 such that operation of the slip control can still bemaintained even during high speed operation when traveling from oneworking site to another.

FIG. 4 illustrates an alternate embodiment of a hydraulic slip controlfor a scraper 71 which has a pair of wheels 72 which are driven by anengine 73. The scraper is drawn by a two wheel tractor 74 which has apair of wheels 76 which are driven by an engine 77. Once again thecontrol is provided for the purpose of detecting and limiting slip ofthe scraper wheels 72 which are in a position remote from the vehicleoperator and therefore difficult for him to view. Engine 77 drives ahydraulic pump 78 at a speed proportional to the speed of wheels 76while engine 73 drives a pump 79 at a speed proportional to the speed ofwheels 72. The output of pump 78 is delivered via a conduit 81 to oneend of a valve 82 which communicates via a conduit 83 with a sump 84from which pump 78 draws its working fluid. The conduit 83 has arestrictive orifice 86 therein to regulate the return flow to the sump84. The opposite end of valve 82 communicates with the output of pump 79via a conduit 87 while a return conduit 88 With a restrictive orifice 89therein returns the flow from conduit 87 to a sump 91 from which pump 79draws its working fluid. Valve 82 includes a slidable spool 92 which hasa land 93 facing the end of valve 82 which receives the output from pump78 and a larger land 94 which faces the end of valve 82 which receivesthe output from pump 79. When wheels 72 and wheels 76 are both travelingat ground speed the output from pumps 78 and 79 will be equal such thatthe pressure on either end of spool 92 will also be equal and the valvespool 92 will be centrally disposed within the valve housing 96. Passingthrough the center of valve 82 is a conduit 97 which communicates at oneend with servo 98 which controls linkage 99 connected to the enginespeed control mechanism of engine 73, and at its other end to a sump(not shown) in the engine 73. A conduit 101 from engine 73 provideshydraulic fluid to conduit 97 at a location between servo 98 and valve82. When the wheels 76 and 72 are traveling at the same speeds and valvespool 92 thereby centered within valve housing 96, the fluid pumpedthrough conduit 181 will return freely to the sump from which it isdrawn through conduit 97 without exerting pressure on servo 98. If,however, wheels 72 slip and thereby drive pump 79 at a speed greaterthan that of pump 78, pressure will build up behind land 94 shiftingspool 92 to the left so as to restrict or block the passage of fluidthrough conduit 97 and thereby enable pressure to build up in conduit 97so as to operate servo 98 to reduce the speed of engine 73. A bypassconduit 182 is provided between conduit 191 and conduit 97 to enable theslip control mechanism to be removed from the vehicle when its operationis undesirable. An electrically operated valve 103 opens and closescommunication between conduits 101 and 102 from a position within theoperators compartment so that the disposition of the control mechanismcan be easily selected by the vehicle operator. If pump 78 shouldoperate at a greater speed than pump 79, spool 92 would shift to theright, but because of the small size of land 93, conduit 97 would not berestricted or blocked.

Referring to FIG. 5, a four wheel tractor 111 includes an engine 112which drives a pair of rear wheels 113 through a drive shaft 114. Driveshaft 114 operatively connects with engine 112 through a transmissiongenerally shown at 116 which operates at a speed proportional to thespeed of wheels 113. A pump 117 is driven by transmission 116 and at aspeed proportional thereto. The output from pump 117 is deliveredthrough conduit 118 to a conduit 119 leading to servo 121 which operateslinkage 122 associated with the vehicle engine speed control mechanism.A conduit 123 also connects with conduit 118 and leads to a fluid motor124 which returns the fluid delivered thereto via conduit 127 to thesump 126 from which pump 117 draws its Working fluid. The speed of motor124 is restricted to the speed of the front wheels 128 of the tractor111 so as to furnish a ground reference speed for the hydraulic controlsystem. Motor 124 is restricted in its operating speed for the reasonsexplained with reference to the embodiment of FIGS. 1 and 2. Theembodiment of FIG. 5 operates through a flexible drive shaft 129 whichis driven by the wheels 128 through a connection therewith generallyindicated at 131. Shaft 129 connect-s to motor 124 so as to limit itsspeed to be proportional to the ground speed of wheels 128. When wheels113 begin to slip the pump 117 delivers more fluid than is passed bymotor 124 under non-slip operating conditions resulting in fluidpressure build up in conduit 119 causing servo 121 to rotate linkage 122and decrease the speed of the engine 112.

In the various embodiments described above it is noted that both fluidpumps and fluid motors have been employed as means for establishingpressures which are proportional to the ground speed of the vehicle. Forthis reason the invention is not limited to either hydraulic motors ofhydraulic pumps exclusively but rather employs the device having themost advantageous operating characteristics under the particularoperating conditions.

We claim: 1. In a power driven vehicle having at least two sets ofwheels at least one of which is driven by an engine, the combinationcomprising:

a hydraulic fluid pump mechanically associated with the engine anddriven at a speed proportional thereto;

hydraulic means disposed to receive the output of said pump and operableto limit the flow of fluid through said means to a rate proportional tothe ground speed of the vehicle, even when the wheels driven by theengine slip;

means operable to regulate the operating speed of the engine; and

means communicating with the output of said pump and said engine speedregulating means and responsive to a rise in pressure at the output ofsaid pump due to slippage of the power driven wheels to reduce theoperating speed of the engine.

2. In a power driven vehicle having at least two sets of wheels at leastone of which is power driven by an engine the combination comprising:

a hydraulic fluid pump mechanically associated with the one set ofwheels to operate at a speed proportional to the speed thereof;

a hydraulic means disposed to receive the output of said pump and allowthe fluid to pass therethrough, said means associated with the other setof wheels and controlled thereby to limit fluid flow through said meansto a rate proportional to the speed of those wheels;

means operable to regulate the speed of the engine;

and

means communicating with the output of said pump and said engine speedregulating means, said means responsive to a rise in pressure at theoutput of said pump due to slippage of said power driven wheels, tocause said regulating means to reduce the operating speed of the engine.

3. The system of claim 2 further including valve means disposed betweensaid pump and hydraulic means and selectively operable to cause theoutput of said pump to be bypassed around said hydraulic means whenoperation of the system is not desired.

4. In a hydraulic clip control system for a tractor drawn scraperwherein the tractor has a pair of power driven wheels and the scraperhas a pair of non-power driven wheels the combination comprising:

a hydraulic pump mechanically associated with the tract-or to operate ata speed proportional to the speed of the power driven wheels thereof;

a fluid motor mechanically associated with one of the non power drivenwheels of the scraper so as to be restricted to an operating speedproportional to the speed of the scraper wheels;

means communicating the output of said pump with said fluid motorwhereby said motor is driven by the fluid from said pump;

means operable to regulate the speed at which the tractor wheels aredriven, said means communicating with the output of said pump andresponsive to a rise in pressure at the output of said pump due toslippage of the tractor wheels to reduce the speed at which the wheelsare driven.

5. The control system of claim 4 .further including:

valve means disposed between said pump and said motor and selectivelyoperable to divert fluid from said pump away from said motor whenoperation of said control is not desired.

6. The control system of claim 4 wherein the mechanical associationbetween said motor and the scraper wheel includes a one-way clutch meanswhich operates to connect said motor to the wheel when the fluid fromsaid pump is capable of driving said motor faster than the speed of thescraper wheels will allow it to operate and disconnect the motor fromthe wheel when the wheel speed is such as to overrun said motor.

7. In a hydraulic slip control for a tractor drawn scraper wherein thetractor has a pair of power driven wheels and the scraper has a pair ofpower driven wheels the combination comprising:

a first hydraulic pump mechanically associated with the tractor anddriven at a speed proportional to the speed at which the wheels of thetractor are driven;

a second hydraulic pump mechanically associated with the scraper anddriven at a speed proportional to the speed of the scraper wheels;

means communicating the output of said second pump with the input ofsaid first pump whereby the pressure at the output of said second pumpis relatively constant when the tractor drawn scraper is moving andneither set of wheels is slipping;

means associated with the scraper and operable to regulate the speed atwhich the scraper wheels are driven; and

means associated with said second pump and said wheel speed regulatingmeans and responsive to a rise in pressure at the output of the secondpump due to the scraper wheels slipping to cause said regulating meansto reduce the speed at which the scraper wheels are driven.

8. In a hydraulic slip control for a four wheel engine driven tractorhaving a set of driven wheels and a set of 7 non-driven wheels thecombination comprising:

a hydraulic fluid pump mechanically associated with, and driven by theengine so as to be driven at a speed proportional to the speed at whichthe driven wheels are driven;

a fluid operated motor communicating with, and driven by the output ofsaid pump;

means mechanically connecting said motor to the nondriven wheels tolimit the motor speed to a speed proportional to the speed of thenon-driven wheels and thereby establish a ground speed reference;

regulating means associated with the engine and operable to regulate thespeed thereof;

servo means communicating with said regulating means and said pump andresponsive to the pressure at the output of said pump rising above thatwhich exists when the driven Wheels are driven at ground speed 5 toinduce said regulating means to decrease the speed of the engine.

References Cited by the Examiner UNITED STATES PATENTS 10 2,170,7668/1939 Rieger 105-48 3,014,764 12/1961 Heckendorf 303-21 3,061,03010/1962 Shallenberg 18077 X A. HARRY LEVY, Primary Examiner.

7. IN A HYDRAULIC SLIP CONTROL FOR A TRACTOR DRAWN SCRAPER WHEREIN THETRACTOR HAS A PAIR OF POWER DRIVEN WHEELS AND THE SCRAPER HAS A PAIR OFPOWER DRIVEN WHEELS THE COMBINATION COMPRISING: A FIRST HYDRAULIC PUMPMECHANICALLY ASSOCIATED WITH THE TRACTOR AND DRIVEN AT A SPEEDPROPORTIONAL TO THE SPEED AT WHICH THE WHEELS OF THE TRACTOR ARE DRIVEN;A SECOND HYDRAULIC PUMP MECHANICALLY ASSOCIATED WITH THE SCRAPER ANDDRIVEN AT A SPEED PROPORTIONAL TO THE SPEED OF THE SCRAPER WHEELS; MEANSCOMMUNICATING THE OUTPUT OF SAID SECOND PUMP WITH THE INPUT OF SAIDFIRST PUMP WHEREBY THE PRESSURE AT THE OUTPUT OF SAID SECOND PUMP ISRELATIVELY CONSTANT WHEN THE TRACTOR DRAWN SCRAPER IS MOVING AND NEITHERSET OF WHEELS IS SLIPPING; MEANS ASSOCIATED WITH THE SCRAPER ANDOPERABLE TO REGULATE THE SPEED AT WHICH THE SCRAPER WHEELS ARE DRIVEN;AND MEANS ASSOCIATED WITH SAID SECOND PUMP AND SAID WHEEL SPEEDREGULATING MEANS AND RESPONSIVE TO A RISE IN PRESSURE AT THE OUTPUT OFTHE SECOND PUMP DUE TO THE SCRAPPER WHEELS SLIPING TO CAUSE SAIDREGULATING MEANS TO REDUCE THE SPEED AT WHICH THE SCRAPER WHEELS AREDRIVEN.